This invention relates to solid state optical waveguides, and more particularly to a waveguide construction in III-V semiconductor material.
Gallium arsenide (GaAs) and indium phosphide (InP) represent two types of semiconducting materials widely used as substrate materials for the fabrication of microwave, high-speed and optoelectronic devices and circuits. Optoelectronic devices such as lasers and detectors are fabricated on heterostructures grown epitaxially on GaAs and InP substrates. Although many of these optical devices can be fabricated on the same wafer (chip), it remains very difficult to connect them together in the same way as one can with electronic devices in silicon integrated circuits.
It is known to use optical connecting paths in the form of waveguides to transport optical signals from one place to another on the chip. However, the fabrication of optical waveguides usually requires an etching process that generates step heights on the order of a micrometer (.mu.m) on the chip surface. Not only is this process difficult to control, but also the resulting steps on the wafer surface present a major obstacle to integrate optical devices monolithically as further lithographic processes to be performed on the uneven wafer surface are difficult to control accurately.
One prior technique to circumvent the step height problem in the fabrication of optical waveguides has involved the implantation of protons into GaAs. The method works by reducing the carrier concentration in the implanted region, thereby increasing its refractive index and hence creating a waveguide structure. However, this technique suffers from two major drawbacks: (1) the substrate to be implanted into has to have a large carrier concentration so that after the implantation, the implanted region can experience a major reduction of carriers in order to result in a sufficient increase of refractive index above that of its surroundings, and (2) the implanted protons tend to diffuse to neighboring regions when the wafer is heated to moderate temperatures, thus undoing the effects of implantation in the intended locations.
What is needed is a mechanism for minimizing the drawbacks of prior techniques while addressing the step height problem.
A precursor to the present invention was described in a paper authored by the inventor and assisted by Y. W. Hui, D. J. Han, and G. H. Li entitled: "Modification of Refractive Index of GaAs by Ion Implantation of Oxygen," Nuclear Instruments and Methods in Physics Research, Sect. B, (NIM B), Vol. 83, pp. 177-180 (1993), North-Holland (Elesvier Science Publishers, B.V., Amsterdam). The content of the article is incorporated herein by reference and made a part hereof. The article did not explore the details of the implantation, the doses or the annealing process.